Lighting apparatus

Abstract

The invention relates to a lighting apparatus comprising a conversion material ( 2 ) for converting primary light ( 4 ) into secondary light ( 5 ), wherein the conversion material ( 2 ) comprises converting photolummescent material ( 15 ), which degrades to non-converting photolummescent material over time when the conversion material ( 2 ) is illuminated by the primary light ( 4 ). The conversion material ( 2 ) is adapted such that, when the conversion material ( 2 ) is illuminated by the primary light ( 4 ), the relative decrease in concentration of the converting photolummescent material ( 15 ) within the conversion material ( 2 ) is larger than the relative decrease in intensity of the secondary light ( 5 ). This allows the lighting apparatus to provide an only slightly reduced absorbance of the primary light, even if a large part of the photolummescent material has been bleached, and thus a longer lifetime, with the same or a slightly reduced intensity of the secondary light.

The invention claimed is: 
     
       1. A lighting apparatus comprising:
 a conversion material for converting primary light into secondary light, wherein the conversion material comprises converting photoluminescent material which degrades to non-converting photoluminescent material over time when the conversion material is illuminated by the primary light, 
 a primary light source for emitting the primary light for being directed to the conversion material for generating the secondary light, 
 wherein the conversion material is adapted such that, when the conversion material is illuminated by the primary light, the relative decrease in concentration of the converting photoluminescent material within the conversion material is larger than the relative decrease in intensity of the secondary light. 
 
     
     
       2. The lighting apparatus as defined in  claim 1 , wherein the conversion material is adapted such that, when the relative decrease in concentration of the converting photoluminescent material is 90 percent, the relative decrease in intensity of the secondary light is smaller than 10 percent. 
     
     
       3. The lighting apparatus as defined in  claim 1 , wherein the converting photoluminescent material comprises an organic photoluminescent material and/or quantum dots. 
     
     
       4. The lighting apparatus as defined in  claim 1 , wherein the primary light source is a light emitting diode. 
     
     
       5. The lighting apparatus as defined in  claim 1 , wherein the conversion material comprises particles for scattering the secondary light for reducing waveguiding effects. 
     
     
       6. The lighting apparatus as defined in  claim 1 , wherein the conversion material forms a layer comprising a decoupling outer surface for coupling the secondary light out. 
     
     
       7. The lighting apparatus as defined in  claim 1 , wherein the conversion material forms a layer comprising a surface being optically coupled to a scattering surface for reducing waveguiding effects. 
     
     
       8. The lighting apparatus as defined in  claim 1 , wherein the conversion material forms a layer comprising an outer decoupling surface for decoupling the secondary light from the layer, wherein the primary light source and the layer are arranged such that the primary light illuminates the layer in a direction being transverse or parallel to the outer decoupling surface. 
     
     
       9. The lighting apparatus as defined in  claim 1 , wherein the lighting apparatus comprises a shield for shielding the converting photoluminescent material from environmental light. 
     
     
       10. The lighting apparatus as defined in  claim 1 , wherein the lighting apparatus comprises a reflective chamber comprising a reflective inner surface for directing the primary light to at least one of a photoluminescence region in which the conversion material is located or an exit window of the reflective chamber. 
     
     
       11. The lighting apparatus as defined in  claim 1 , wherein the converting photoluminescent material is arranged in a pattern. 
     
     
       12. The lighting apparatus as defined in  claim 11 , wherein the pattern comprises at least one first area with the converting photoluminescent material and at least one second area without the converting photoluminescent material. 
     
     
       13. The lighting apparatus as defined in  claim 11 , wherein the conversion material comprises a composite including two phases and wherein the converting photoluminescent material is present in one of the two phases only for arranging the converting photoluminescent material in the pattern. 
     
     
       14. A manufacturing method for manufacturing a lighting apparatus, the manufacturing method comprising:
 providing conversion material for converting primary light into secondary light, wherein the conversion material comprises converting photoluminescent material, which degrades to non-converting material over time when the conversion material is illuminated by the primary light, 
 adapting the conversion material such that, when the conversion material is illuminated by the primary light, the relative decrease in concentration of the converting photoluminescent material within the conversion material is larger than the relative decrease in intensity of the secondary light, 
 providing a primary light source for emitting the primary light, 
 arranging the conversion material and the primary light source such that the primary light is directable to the conversion material for generating the secondary light. 
 
     
     
       15. A lighting method, wherein primary light is emitted by a primary light source and directed to conversion material comprising converting photoluminescent material, which degrades to non-converting photoluminescent material over time when the conversion material is illuminated by the primary light, for generating secondary light, wherein the conversion material is adapted such that, when the conversion material is illuminated by the primary light, the relative decrease in concentration of the converting photoluminescent material within the conversion material is larger than the relative decrease in intensity of the secondary light.